I. Field of the Invention
The present invention relates to a method and apparatus for cleaning a storage tank for petroleum products.
II. Description of the Prior Art
In industrial applications, petroleum products are typically stored in large storage tanks. These large storage tanks typically include a closed cylindrical sidewall which forms the reservoir for the petroleum products. A floating roof is then disposed across and covers the open top of the reservoir. These floating roofs, however, float upon the petroleum products contained within the storage tank so that the vertical position of the floating roof varies in accordance with the amount of petroleum products in the storage tank.
The floating roof of the storage tank typically includes a number of radially spaced and vertically extending openings. Each of those radially spaced openings is adapted to removably receive a leg so that, with the leg positioned within the opening and secured to the floating roof, the leg depends downwardly from the floating roof by a predetermined distance, e.g. three feet or six feet. Consequently, when the tank is nearly empty, these legs engage the bottom of the storage tank and prevent the floating roof of the storage tank from contacting the bottom of the storage tank. The floating roof of the storage tank can also include other openings, such as an access opening.
After prolonged use, dirt, waxes and other petroleum distillates tend to accumulate along the bottom of the storage tank. This accumulation at the bottom of the storage tank must be periodically cleaned in order to enable proper functioning of the storage tank.
There have been a number of previously known methods for cleaning the accumulation at the bottom of the storage tank. In one method, one or more openings are formed through the sidewall of the storage tank adjacent its bottom. Petroleum products under high pressure are then pumped through these openings which emulsify the accumulation at the bottom of the storage tank so that the petroleum products with the emulsified accumulation can be pumped and thus removed from the tank.
One disadvantage of this previously known method, however, is that it requires the sidewall of the tank to be breached which is not only expensive, but also may adversely affect the integrity of the tank. Furthermore, while this previously known method is adequate for emulsifying the accumulation adjacent the sidewalls of the tank, it is only partially effective for removing the accumulation near the center of the tank due to the reduced pressure of the injected petroleum products at the center of the tank.
A still further previously known method for cleaning the storage tank is to physically enter the storage tank and manually remove the accumulation. This method, however, is time consuming and very expensive.